1. Field of the Invention
The present invention relates to an X-ray simulating method and system for a radiotherapy planning for obtaining radiotherapy simulation data.
2. Description of the Related Art
In radiotherapy, generally, a therapy planning is made prior to execution of the therapy, and the therapy is executed on the basis of the therapy planning to obtain effective clinical results. Such a radiotherapy planning essentially includes at least a process of acquiring correct geometrical information concerning a diseased part (focus) and a process of determining proper radiation conditions on the basis of the geometric information (a radiotherapy simulation data determination process).
A typical example of an apparatus for use in the radiotherapy planning is an X-ray simulator, and an X-ray simulator of this type is basically an X-ray imaging apparatus. A conventional X-ray simulator will be described below with reference to FIG. 1.
As shown in FIG. 1, this conventional X-ray simulator is an apparatus capable of setting an X-ray tube 10 and an X-ray image acquiring unit 20 at desired positions where they oppose each other with a patient 30 sandwiched therebetween. The X-ray generator 10 comprises an X-ray tube 12 and a limiting unit 14. The limiting unit 14 is constituted by at least an X-ray diaphragm, a simulation collimator (wire collimator) and a simulation scale.
The X-ray image acquiring unit 20 generally comprises a system for acquiring a fluoroscopic image and a system for acquiring a radiographic image. The fluoroscopic image is a TV image used as a positioning image for confirming a position for radiographing an X-ray film image. The radiographic image is an X-ray film image used as an image for obtaining geometrical data of a diseased part. Images of a diseased part 32, the wire collimator, and the simulation scale are formed on the X-ray film image. Note that the patient 30 is placed on a tabletop 40.
The X-ray generator 10 and the X-image acquiring unit 20 of the X-ray simulator are set to oppose each other in POSITION "A" as shown in FIG. 1, and an X-ray film image 50 of a patient at POSITION "A" is acquired while a fluoroscopic image is observed. Subsequently, the X-ray generator 10 and the X-ray acquiring unit 20 of the X-ray simulator are set to oppose each other in POSITION "B" as shown in FIG. 1, and a radiographic image (X-ray film image) 52 of the patient 30 at POSITION "B" is acquired while the fluoroscopic image is observed. The X-ray radiation directions are different from each other by a predetermined angle such as 90.degree. at POSITION "A" and POSITION "B".
On the X-ray film image 50 acquired at POSITION "A", a diseased part image 50A, an image of a portion except for the diseased part, and reference images such as a wire collimator image 50B and a simulation scale image 50C are formed. On the X-ray film image 52 acquired at POSITION "B", a diseased part image 52A, an image of a portion except for the diseased part, and reference images such as a wire collimator image 52B and a simulation scale image 52C are formed.
An operator obtains geometrical information of the diseased part 32 by observing the X-ray film images 50 and 52 while referring to the fluoroscopic images at POSITION "A" and POSITION "B". In this case, the operator observes the X-ray film images 50 and 52 by associating the diseased part images 50A and 52A, the images of the portion except for the diseased part, and the reference images such as the wire collimator images 50B and 52B and the simulation scale images 50C and 52C, respectively formed on the X-ray film images 50 and 52, with one another.
On the basis of the geometrical information of the diseased part 32, the operator forms simulation data for radiotherapy, which determines radiation conditions such as the type, the radiation field, and the radiation direction of rays for use in the therapy. This simulation data is supplied to a radiation therapy apparatus such as Linear accelerator, and the radiation therapy apparatus executes radiotherapy on the basis of the input simulation data.
As described above, the X-ray simulator used in a conventional radiotherapy plan simply provides X-ray film images for obtaining geometrical information of a diseased part. An operator obtains geometrical information of a diseased part from the X-ray film images and forms radiotherapy simulation data on the basis of the geometrical information of the diseased part. The operator forms the radiotherapy simulation data for determining radiation conditions by manually operating an instrument such as the limiting unit 14 of the X-ray simulator or an instrument such as a limiting unit of a radiation therapy apparatus, or by manually operating a patient table of the X-ray simulator or that of the radiation therapy apparatus.
This manual operation is constituted by a plurality operations. Therefore, formation of the radiotherapy simulation data is difficult and incorrect. For example, a limiting aperture is determined by the eye on the basis of geometrical information of a diseased part. Therefore, a trial-and-error operation must be performed a large number of times to determine an optimal radiation field capable of minimizing a radiation dose to a normal part of a patient. If the number of operation times is small, on the other hand, the operation precision is degraded.